The present invention relates to implantable cardioverter defibrillators (ICDs), and more particularly to an ICD that automatically determines the most effective sensing electrode configuration.
An implantable cardioverter defibrillator provides therapies for maintaining and restoring normal cardiac rhythms by pacing or by delivering electrical shock therapy for cardioverting or defibrillating the heart. The ICD is implanted pectorally, and one or more electrical leads connected to the ICD are inserted into or in proximity to the heart of the patient. The leads carry current from the ICD to the heart tissue to stimulate the heart using either low energy pacing pulses or high energy cardioversion/defibrillation shocks. The leads are also used for sensing electrogram (EGM) signals from the heart that are used by the ICD to determine therapy to be delivered.
Within the ICD, sense amplifiers coupled to the leads amplify electrogram signals from the electrodes. The amplified EGM signal is filtered, rectified, and level-detected to sense intrinsic depolarizations of the atria (referred to as P-waves) and the ventricles (referred to as R-waves).
Single chamber ICDs use a single lead placed in the right ventricle to treat ventricular arrhythmia. Dual chamber ICDs treat ventricular arrhythmia (and in some cases atrial arrhythmia as well), and include one lead placed in the right ventricle and a second lead placed in the right atrium. In some cases, a third lead may be placed to gain access to the left ventricle (e.g. in the coronary sinus).
The ICD leads include a tip electrode that is attached to the wall or surface of the heart and a ring electrode that is located on the lead but spaced a short distance from the tip electrode. The ring and tip electrodes form a bipolar electrode pair for pacing and for sensing.
A high voltage coil used for delivering a cardioversion/defibrillation shock is also located on the ventricular lead. Some right ventricular leads carry two coils, one located in the right ventricle and the other located in the superior vena cava (SVC). A high voltage shock is typically applied between one of the high voltage coils and electrically conductive housing or can of the ICD.
The tip and ring electrodes of the lead are typically used for sensing EGM signals using a true bipolar sensing configuration. In some leads, the ring electrode is not present in order to reduce the number of conductors. In that case, the high voltage coil and the tip form an EGM sensing configuration which is referred to as integrated bipolar sensing. With improved lead technology, leads having a ring electrode, a tip electrode, and one or two high voltage coils are being used to a greater extent. These leads have the capability for both true bipolar sensing or integrated bipolar sensing. Current ICDs/leads provide for just one type of sensing.
For dual chamber detection algorithms in ICDs, based upon the sensed P-waves from the atrial lead and R-waves from the ventricular lead, the ICD delivers a therapy, which can include antitachycardia pacing (ATP), cardioversion or defibrillation. The effectiveness of the ICD in treating tachyarrhythmia depends upon the ability to accurately sense P-waves and R-waves with the atrial and ventricular leads, respectively. Oversensing of R-waves can produce an erroneous identification of ventricular tachycardia or fibrillation, resulting in unnecessary and painful cardioversion/defibrillation shocks and a waste of battery energy. Conversely, undersensing of R-waves can result in failure to detect ventricular tachycardia or fibrillation, and therefore failure to provide therapy when needed.